Effects of age on nutrient digestibility in chicks fed different diets

Three experiments were conducted to determine the effects of age on apparent ME(n) and apparent amino acid (AA) digestibility of various diets for New Hampshire x Columbian (Experiments 1 and 2) and commercial broiler (Experiment 3) male chicks. Excreta were collected at 0 to 2, 3 to 4, 7, 14, and 21 d of age in all experiments, and nutrient digestibility was determined using acid-insoluble ash as a marker. The first experiment evaluated a corn-soybean meal (SBM) diet. Both ME(n) and digestibility of AA increased with age, and broken-line regression analysis predicted a plateau at 14 d for ME(n) and 10 d of age for AA digestibility. For example, ME(n) increased from 2,970 to 3,430 kcal/kg DM, and lysine digestibility increased from 78 to 89% between 0 and 14 d of age. The second experiment evaluated cornstarch-crystalline AA, dextrose-casein, corn-SBM, and corn-canola meal diets. The ME(n) of the corn-SBM, corn-canola meal, and cornstarch-crystalline AA diets increased from 0 to 14 d of age. In contrast, the ME(n) of the dextrose-casein diet was high (3,800 kcal/kg DM) immediately after hatching and did not increase substantially with increasing age. Digestibility of AA increased with age for the corn-SBM and corn-canola meal diets, and broken-line regression analysis again predicted a plateau at approximately 10 d of age. Conversely, AA digestibility of the dextrose-casein and cornstarch-crystalline AA diets was high immediately after hatching (93 to 96%) and increased only slightly with age. The results of Experiment 3 with commercial broiler chicks also showed significant (P < 0.05) increases in ME(n) and AA digestibility with increasing age. The results of this study indicated that the ME(n) and AA digestibility of corn-SBM and corn-canola meal diets increase with age for young chicks. The results also showed that ME(n) and AA digestibility were very high for a dextrose-casein diet immediately after hatching. Thus, the latter ingredients may have beneficial effects for very young chicks.